[FFmpeg-devel] [PATCH] add silenceremove filter

[Paul B Mahol]

On 8/31/14, Timothy Gu <timothygu99 at gmail.com> wrote:
> On Aug 29, 2014 11:23 AM, "Paul B Mahol" <onemda at gmail.com> wrote:
>>
>> Signed-off-by: Paul B Mahol <onemda at gmail.com>
>> ---
>>  doc/filters.texi               |  62 ++++++
>>  libavfilter/Makefile           |   1 +
>>  libavfilter/af_silenceremove.c | 478
> +++++++++++++++++++++++++++++++++++++++++
>>  libavfilter/allfilters.c       |   1 +
>>  4 files changed, 542 insertions(+)
>>  create mode 100644 libavfilter/af_silenceremove.c
>>
>> diff --git a/doc/filters.texi b/doc/filters.texi
>> index cca15fc..ea7da88 100644
>> --- a/doc/filters.texi
>> +++ b/doc/filters.texi
>> @@ -1881,6 +1881,68 @@ ffmpeg -i silence.mp3 -af
> silencedetect=noise=0.0001 -f null -
>>  @end example
>>  @end itemize
>>
>> + at section silenceremove
>> +
>> +Removes silence from the beginning, middle or end of the audio.
>> +
>
> @subsection Options

No other filters do that.

>
>> +The filter accepts the following options:
>> +
>> + at table @option
>> + at item start_periods
>
>> +This value is used to indicate if audio should be trimmed at beginning
>> of
>> +the audio.
>
> ... and how much silence to trim.
Nope, it does not tell how much to trim, it trims all silence up to noise.

>
>> A value of zero indicates no silence should be trimmed from the
>> +beginning.
>
>> When specifying an non-zero value, it trims audio up until it
>> +finds non-silence. Normally, when trimming silence from beginning of
> audio
>> +the @var{start_periods} will be @code{1} but it can be increased to
> higher
>> +values to trim all audio up to specific count of non-silence periods.
>
> Is this better?
>
> ---
> When a nonzero value is specified, audio is trimmed until the specified
> count of non-silence periods is reached.
>
> Normally you would use 1 which means that trimming is stopped as soon as
> non-silence is reached.
> ---

I prefer original text from sox manual.

>
> What if I have an audio segment like this, with start_periods==2 and
> start_duration==4? What will get trimmed and what will not?
>
> Silence5sec Noise1sec Silence2sec Noise5sec Silence5sec Noise5sec
> Silence1sec NoiseForever

It would trim up to 2nd silennce and would also trim 4 seconds from 5 seconds
of noise5sec.

>
>> +
>> + at item start_duration
>> +Specify amount of time that non-silence must be detected before it stops
>
>> +trimming audio. By increasing the duration, burst of noise can be
>> treated
>
> bursts of noises

Changed.

>
>> +as silence and trimmed off.
>> +
>
>> + at item start_threshold
>
>> +This indicate what sample value should be treated as silence. For
>> digital
>
> indicate_s_ how "silent" a segment must be to be treated as silence.

Done.

>
>> +audio, a value of @code{0} may be fine but for audio recorded from
> analog,
>> +you may wish to increase the value to account for background noise.
>
>> +
>> + at item stop_periods
>> +Set the count for trimming silence from the end of audio.
>> +To remove silence from the middle of a file, specify a
>> @var{stop_periods}
>
>> +that is negative. This value is the threated as a positive value and is
> also
>
> threated

Done.

>
>> +used to indicate the effect should restart processing as specified by
>> + at var{start_periods}, making it suitable for removing periods of silence
>> +in the middle of the audio.
>> +
>> + at item stop_duration
>> +Specify a duration of silence that must exist before audio is not copied
> any
>> +more. By specifying a higher duration, silence that is wanted can be
>> left
>> +in the audio.
>> +
>> + at item stop_threshold
>
>> +This indicate what sample value should be treated as silence but for
>> +trimming silence from the end of audio.
>
> This the same as @option {start_threshold} but for trimming...

Changed.

>
>> +
>> + at item leave_silence
>> +This indicate that @var{stop_duration} length of audio should be left
> intact
>> +at the beginning of each period of silence.
>> +For example, if you want to remove long pauses between words but do not
> want
>> +to remove the pauses completely.
>> +
>> + at end table
>> +
>> + at subsection Examples
>> +
>> + at itemize
>> + at item
>> +The following example shows how this filter can be used to start
> recording
>> +that does not contain the delay at the start which usually occurs
>> between
>
>> +pressing the record button and the star of the performance:
>
> start

Done.

>
>> + at example
>> +silenceremove=1:5:0.02
>
> What are these values? I.e. can you show is in a named form too?

I could but this is shorter.

>
>> + at end example
>> + at end itemize
>> +
>
> More review might follow if you answer my question above.
>
> Timothy
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